Here's a fun way to add a cute design to a plain tee, all you need is some basic free-hand drawing practice and some fabric paint.
You will need :

A plain cotton tee
A paint brush and fabric paints
Long and wide magazine or piece of cardboard
Newspaper
An iron
A crayon

Step 1: Draw It Out

Picture your design first if you want to make a different doodle or you can just follow my drawing if you want this one.Just draw it out on some paper so you can refer to it later it helps make your final design neater.

Step 2: Mark Your Design

Tuck the card board in the newspaper and slip into the shirt. Use a crayon to copy your design on your shirt . Try to use a single line with no breaks to get the doodle effect with only slight curves.

Step 3: Paint It

Nows the fun part, just trace over your crayon with a thin paint brush. Try to keep your lines clean with no breaks or splotches. Let it dry for about four hours or depending on your paints instructions.

Step 4: Set It

After drying for about 24 hours, flip your shirt inside out and iron on high for about a minute to set the paint.Put your shirt in the wash to see how the paint stands up. The crayon will wash off.If the paint fades or gets scratched a bit apply another coat and iron it again if you want.

That's it you now have a simple but cute new shirt. Try different animals or designs and post a comment below and lemma know what you think.